The present invention relates to a fluidizing gravity conveyor for conveying finely divided material in an inclined path, and, more particularly, deals with an apparatus adapted for the conveyance, by gravitational force, of such materials while at elevated temperatures and while in a state of fluidity induced by the passage of a gas, such as air, through the material. The invention further comprises a fluid distributor member having a conveying surface for use in such a conveyor, wherein the fluid distributor has substantially uniform gas-permeability and through which gas is passed from an underlying plenum chamber into the overlying finely divided material to fluidize the material so that it will flow by gravity downwardly along the gas-permeable surface. More particularly the invention comprises a fluidizing gravity conveyor for conveying finely divided material that is particularly designed for conveying high temperature material including material having temperatures ranging from about 500° F. to about 2900° F. and, most typically, material having temperatures from about 1200° F. to about 1800° F.
It is known to utilize a conveying apparatus for finely divided material such as alumina, cement raw meal, finish cement and the like, wherein a conveying conduit includes a gas permeable member dividing the conduit into an upper material chamber and a lower plenum chamber. The conduit includes an inlet at one end for supplying material to be conveyed to the material chamber and an outlet end for discharging material from the conduit. Gaseous fluid under pressure, such as air, is supplied to the lower plenum chamber for passage upwardly through the gas permeable member. Material supported on the gas permeable member in the material chamber is aerated and fluidized by the gas under pressure. When fluidized, the material will flow downwardly from the inlet to the outlet by gravity. Usually, the conveying apparatus is set at a small slope such as 6°, to facilitate material flow, although larger slopes may be utilized for a particular application. (In plant practice the slope of the conveyor is generally dictated by the headroom available.)
There is a need for a fluidized conveyor to efficiently convey finely powered material in high temperature industrial applications, for example as in conjunction with preheaters utilized in the cement manufacturing process. The use of such a conveyor can serve to lower the preheater tower height at cement plants. Typically, such preheaters consist of a plurality of serially connected cyclone separators with material being alternately entrained in the hot gases and separated by the cyclones to thereby preheat the material to as much as 1500° F. or 1600° F.
Most fluidizing gravity conveyers utilize tightly woven aeration fabric with closely controlled air porosity as the gas permeable member to distribute the fluidizing area to the material chamber. This is generally satisfactory for most applications; however typical aeration fabrics used for fluidizing gravity conveyors have a maximum temperature of 500° F. and are not suitable to evenly distribute a cold fluid from a plenum chamber to an adjacent high temperature material chamber. If high temperature materials are to be conveyed with a fabric gas permeable member the fabric may ignite and destroy the conveyor. Many commercially available porous materials otherwise suitable for use in ambient conditions can not withstand the high temperature or the thermal shock (defined as large thermal stresses caused by the large temperature differential between the material chamber and the plenum chamber as seen by the opposing sides of the distributor member). Alternatively, high temperature insulation is a porous material that can withstand the high temperature and temperature gradient, but it erodes away if it is exposed to flowing material.
U.S. Pat. No. 4,418,650 shows the use of a distributor consisting of horizontal tubes used for cooling and insulation to protect the distributor from heat. The upper surface of the distributor is not smooth since the fluidizing air passes through tubes protruding through the surface of the distributor. U.S. Pat. No. 4,818,152 teaches a fluidizing gravity conveyor having utility for hot particulate material which includes a heat resistant plate having a plurality of holes for receiving bubble caps or nozzles that protrude above the upper surface of the plate to disperse air flow from a lower plenum chamber to the upper material chamber. The conveyors taught by such patents may not be optimum for certain types of material since the protruding tubes, bubble caps or nozzles may cause such material to clump and form obstructions to the material flow. Therefore, it would be advantageous, and it is an object of this invention, to have a conveyor suitable for high temperature applications that has a smooth upper surface for receiving and conveying material.